US regulators should approve the proposed US$45.2 billion ($52.7 billion) merger of two biggest US cable providers Comcast and Time Warner Cable, but set "clear conditions," Washington Post's editorial board said on Tuesday.

Public interest groups and some lawmakers have opposed a merger, saying it would allow Comcast to raise cable television rates and gain more power over what Americans watch on TV or online.

In Tuesday's newspaper, the newspaper's editorial board said these concerns were not enough for the Federal Communications Commission to "take the severe step" of blocking a deal, but warranted conditions "that allow a crackdown" if cable companies begin to treat competitors and upstarts unfairly.

"The government's smartest move is not to block the merger, but to make clear that regulators will respond if big industry players begin to violate basic principles of market fairness," the editorial said.

The FCC will determine whether the merger is in the public interest and the Justice Department must decide whether it complies with antitrust law.

Comcast last week laid out the arguments in favour of its deal in a lengthy public interest filing at the FCC and then at a congressional hearing.

The company has said its business faces powerful competitors like Google or Apple, and has stressed that Comcast and Time Warner Cable do not directly compete in any market.

The Washington Post laid out some arguments for and against the deal and concluded that the foggy outlook for the future of communications and entertainment "recommends a degree of regulatory caution."